In order to avoid the discontinuous delivery of power to the opposite endless track chains of an earthmoving tractor during turning various differential steering mechanisms have been proposed. One typical differential steering mechanism employs a pair of oppositely disposed planetary gear steering units whose output members rotate the sprockets that drive the track chains. One element of each steering unit is driven by the transmission of the tractor through appropriate gearing to provide the primary drive power path, while another element of each steering unit is driven by an auxiliary system to provide a secondary steering drive power path. A hydraulically driven steering motor delivers power to the oppositely disposed elements or gears by way of a transverse shaft system parallel to the central axis of the mechanism. In operation, one gear at one side of the tractor is rotatably driven at the same speed, but in the opposite direction to a counterpart gear on the other side to effect a turn.
Such prior steering differentials have been relatively complex in construction and costly. One reason for this is that a large vehicle case has been required to contain certain steering components, such as the steering motor and steering shaft system, within it.
Another problem is that when the steering motor is mounted within the vehicle case it is relatively inaccessible for convenient servicing. When the steering motor is mounted externally in order to improve servicing thereof it is difficult to maintain the relationship between its centerline and the centerline of the associated gearing. Specifically, precision boring of the relatively large vehicle case is a costly manufacturing step, and this is especially true when the axes of the related cylindrical openings are arranged at a right angle to each other. If the steering motor is radially oriented relative to the transverse axis of the steering mechanism, which is often particularly desirable in the limited space available in the tractor, the steering power path can be by way of an intermeshing pinion and bevel gear set. However, maintaining the desired gear tooth loading action and amount of backlash in that gear set is difficult when the rotary elements are mounted on spaced apart members which are not only subject to misalignment problems but also to differential deflection of the elements in use.
Accordingly, it would be advantageous to provide a relatively simple steering differential which will have improved structural integrity between the rotary elements thereof, while allowing the steering motor to be mounted generally exteriorly of the case for more convenient servicing and generally at a right angle to the transverse central axis at a particularly desirable location.
The present invention is directed to overcoming one or more of the problems set forth above.